Judging changes in images of the eye

ABSTRACT

The invention includes a computer-implemented method, system ( 100 ), and computer-readable medium having computer-executable modules for judging changes in components of an eye. The inventive computer-implemented method includes the steps of acquiring ( 103 ), displaying ( 107 ), and superimposing at least two digital images of the components of the eye. The method further includes the step of processing at least one of the digital images such that the superimposed images may be compared, and the step of flickering among the superimposed digital images. The step of acquiring the images may include the step of converting a photographic representation of the components of the eye to the digital image. The step of processing may include registering, warping, and/or aligning the digital images.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Patent Application Serial No. 60/171,519, which was filed onDec. 22, 1999, and which is hereby incorporated by reference in itsentirety.

STATEMENT OF GOVERNMENT SUPPORT

This invention was supported by funds from the U.S. Government (NIHGrant No. NIH K08-00374). The U.S. Government may therefore have certainrights in the invention.

FIELD OF THE INVENTION

The invention relates to the field of diagnosis and management of eyediseases or conditions. More specifically, the invention relates to amethod of judging changes in digital images of components parts of theeye to diagnose and manage eye diseases or conditions.

BACKGROUND OF THE INVENTION

Detecting certain diseases or conditions of the eye often requirescomparing photographic representations of the eye's component parts.Typically, such photographs are taken over the course of years bydifferent examiners using different devices. These inevitable variationsoften result in an unavailing comparison that frequently frustrates thediagnosis of blinding diseases, like glaucomatous optic neuropathy(“glaucoma”).

Glaucoma is a blinding disease associated with progressive impairment ofoptic nerve function. Diagnosis and management of the patient with, orat risk for, glaucoma is highly dependent on detecting contour changesin the optic nerve head. Currently, detecting such contour changes inthe clinical environment requires careful visual inspection ofsequential, magnified, stereoscopic optic nerve head photographic imagepairs that have been acquired at distinct instances in time. These imagepairs may be acquired by a standard fundus camera, scanning laserophthalmnoscope, slitlamp camera, or other device capable of imaging theeye or its component parts.

With glaucoma, an examiner uses a stereoscopic viewer to view variousimages of the optic nerve head. Contour changes are observable asapparent differences in depth between the images. Discerning suchchanges through visual inspection, however, is difficult for patientmanagement and clinical research trials. In particular, the examinercannot superimpose the stereoscopic images, but must attempt to do so inhis mind. This endeavor is made more difficult by the requisite timeinterval between captured images (often years), which invariably resultsin different magnification, rotation, position, and warp among thedifferent captured images. As a result, detection of glaucoma using astereoscopic viewer is notoriously difficult. Similarly, changedetection based on images of the eye or its component parts is difficultwhether derived from findus photography, angiography, slitlampphotography, or other sources.

As a result of the difficulty in evaluating stereoscopic images of theoptic nerve head, many clinicians compare visually only the informationavailable on monocular photographs of the optic nerve head. In otherwords, they compare monocular photographic images of the optic nervehead taken over time, typically over the course of years, seeking toidentify changes such as advancing atrophy or altered position of theretinal vessels. The unavoidable variations (e.g., exposure,orientation, and magnification) in photographs obtained over the courseof years limit the diagnostic sensitivity of this manual approach toglaucoma diagnosis.

Goldmann and Lotmar, in extending a technique they termed“stereo-chronoscopy,” proposed that pairing monocular sequentiallyobtained photographic images of the optic disc could improve glaucomadiagnosis and management. Goldmann H. and Lotmar W., Rapid Detection ofChanges in the Optic Disc: Stereo-chronoscopy, Albrecht v. Graefes Arch.klin. exp. Ophthal. 202: 87-99 (1977); Goldmann H. and Lotmar W., RapidDetection of Changes in the Optic Disc: Stereo-chronoscopy. II.Evaluation Technique, Influence of Some Physiologic Factors, andFollow-Up of a Case of Choked Disc., Albrecht v. Graefes Arch. klin.exp. Ophthal. 205: 263-277 (1978). In this technique, monocularphotographic views of the optic nerve head taken at different times wereviewed simultaneously as a pseudo-stereo pair in a stereoscope. Opticdisc change over time theoretically would appear as a pseudo-stereoeffect in these paired images, while stable discs would appear flat tothe observer. This method presupposed the capability of clinicalphotographic and optical methods to obtain images that could later bealigned visually. Because it proved impractical to take optic nervephotographs initially with the alignment precision demanded by thetechnique, stereo-chronoscopy never progressed beyond the initial pilotdevelopment stages.

A number of early studies attempted to improve on stereo-chronoscopy byemploying various alternative means to achieve image superposition. Forexample, Heiji A. and Bengtsson B., Diagnosis of Early Glaucoma withFlicker Comparisons of Serial Disk Photographs, Invest. Ophthalmol andVis. Science 30: 2376-2384 (1984) developed a crude form of flickercomparison by alternating between images from a projector device. Thistechnique also allowed for manual alignment of the projectors to correctfor translational and rotational misalignment between the sequentialimages. The methods of these authors were complex and time-consuming,but they did conclude that flicker analysis could be useful clinically.

Algazi R. V., Keltner J. L., and Johnson C. A., Computer Analysis of theOptic Cup in Glaucoma, Invest. Ophthalmol Vis. Science 26: 1759-1770(1985) also described an early approach based on registration ofsequentially acquired images with a reference image. The user couldcontrol rotation, translation and scale in order to bring these imagesinto alignment. Sequential monocular display then facilitated changedetection. The authors noted that the procedure was very time consumingwhen compared with standard techniques and that results were notreproducible.

Nagin P., Schwartz B., and Reynolds G., Measurement of FluoresceinAngiograms of Optic Disk and Retina Using Computerized Image Analysis92: 547-552, Ophthalmology (1985) registered angiographic optic discimages to permit analysis of vascular filling in these image sequences.Vascular crossing points were identified automatically, andcorrespondence between these points allowed for determination of anaverage translational and rotational displacement vector describing theimage transformation. However, this technique was not formallyvalidated. Moreover, accurate fundus image change detection requiresimage registration beyond that permitted by rigid body transformations(i.e., rotation and translation).

Other methods have been developed that typically using complex opticalinstruments to obtain clinical images and provide quantitative measuresof optic nerve head topography. However, because of their complexity,questionable accuracy, and uncertain diagnostic superiority, none ofthese newer methods has achieved widespread use or acceptance. Moreover,these complex methods often are unable to use archived photographicimages of the patient's optic nerve head, which are important indetecting the progressive changes attributable to glaucoma. Thus,subjective assessment of standard clinical examination and standardfundus photographic images remains the primary method for diagnosingglaucoma

SUMMARY OF THE INVENTION

In view of the above-mentioned limitations in the prior art, theinvention describes a more practical method for detecting and analyzingimages of the eye or its component parts. Although the prior art hasdeveloped from methods for glaucoma diagnosis and management, theinvention has utility in diagnosis and treatment of other eye diseasesas well.

The invention includes a computer-implemented method, system, andcomputer-readable medium having computer-executable modules forassisting in discernment of changes in components of an eye. Theinventive computer-implemented method includes the steps of acquiring,displaying, and superimposing at least two digital images of thecomponents of the eye. The method further includes the step ofprocessing at least one of the digital images such that the superimposedimages may be compared, and the step of flickering among thesuperimposed digital images. The step of acquiring the images mayinclude the step of converting a photographic representation of thecomponents of the eye into the digital image. The step of processing mayinclude registering, warping, and/or aligning the digital images. Thestep of registering the digital images may include the step ofnon-rigid, non-global deforming of the digital images. The step ofwarping may include the step of global and/or non-global deforming ofthe digital images. The step of aligning includes the steps ofnon-rigidly and/or rigidly aligning of the digital images. The methodmay further include the step of detecting changes among the flickered,superimposed digital images, and diagnosing a condition of the eye as afunction of the detected changes. The inventive method further mayinclude the step of selecting at least two of the acquired images.

The invention also includes a system for judging changes in componentsof the eye. The inventive system includes a data processor that receivesand superimposes the digital images of the components of the eye. Thedata processor also processes the digital images to facilitatecomparison among the images. The system also includes a display devicein communication with the data processor for displaying the digitalimages and the superimposed images, and a control unit in communicationwith the data processor for flickering among the superimposed images.The control unit may include a keyboard, a mouse, a joystick, and/or amicrophone, for example. The digital images may be monoscopic imagesthat depict an optic nerve head component of the eye. The system alsomay include an image scanner in communication with the data processorfor converting photographic images of the components of the eye into thedigital images. Also, the system may include a digital image acquisitiondevice in communication with the data processor for acquiring thedigital images. The digital image acquisition device may include adirect ophthalmoscope, slitlamp biomicroscope, and findus camera, forexample. In addition, the system may have a data store in communicationwith the data processor for storing the digital images.

The invention also includes a computer-readable medium havingcomputer-executable modules. The computer-executable modules include aninput module for receiving digital images of the components of the eye,a video module for superimposing the digital images and for displayingthe superimposed digital images on a display, and a control module forflickering among the superimposed digital images. The input module maybe adapted to receive the digital images from an image scanner, and toreceive the digital images directly from a digital image acquisitiondevice. The computer-readable medium may have an image processing modulefor processing at least one of the images, and a data storage module forstoring the digital images.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other novel features and advantages of the inventionwill become more apparent and more readily appreciated by those skilledin the art after consideration of the following description inconjunction with the associated drawings, of which:

FIG. 1 is a block diagram of a system for judging changes in componentsof an eye, according to the invention; and

FIGS. 2A and 2B provide a flowchart of a method for judging changes incomponents of an eye, according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is block diagram of a system 100 for judging changes incomponents of an eye. As shown in FIG. 1, a data processor 101 is incommunication with a digital image acquisition device 103. Dataprocessor 101 may be a part of a typical computer-readable medium, likea desktop computer, for example. Data processor 101 may have modulesand/or computer-executable instructions in the form of software capableof receiving and/or processing digital images of the component parts ofthe eye. Such processing is necessary to align images of the componentparts of the eye taken over time, such that intelligent comparison maybe made for the purposes of detecting and managing diseases of the eye,including glaucoma.

Digital image acquisition device 103 is a device capable of capturingimages of the component parts of the eye in a digital format. Digitalimage acquisition device 103 acquires digital images of component partsof the eye, and provides the digital images to data processor 101.Digital image acquisition device 103 may be a single unit, for examplemodel number NS-1V slitlamp biomicroscope available from Nikon, Inc., asimilar slitlamp biomicroscope available from Topcon, Inc., or similardigital fundus camera. It should also be appreciated that digital imageacquisition device 103 may be an analog image acquisition device coupledto a camera unit (not shown). In this case, the image acquisition devicemay be a direct ophthalmoscope, slitlamp biomicroscope, or funduscamera, for example. The direct ophthalmoscope may be a devicecommercially available from Welch-Allyn, Inc., and the slitlampbiomicroscope may be a device commercially available from Nikon, Inc.,model number NS-1V. The fundus camera may be a FF4 fundus camera,available from Zeiss, Inc. The camera unit (not shown) may be adapted toreceive images from the direct ophthalmoscope and the slitlampbiomicroscope, for example, a charge coupled device (CCD) camera.

Data processor 101 further is in communication with an image scanner109. Image scanner 109 is a device capable of converting a photographicimage into a corresponding digital image having a certain resolution anda certain file format. Image scanner 109 is useful in permittingarchived non-digital images of the component parts of the eye to be usedby the invention, for example 35 mm or Polaroid images. Image scanner109 may be a Scanmaker 35t, available from Microtek, Inc., and capableof creating a digital image in any format and resolution, for example aJoint Photographic Experts Group (JPEG) digital image with a 1000dots-per-inch (dpi) resolution. Digital processor 101 receives thedigital image in the predefined file format (e.g., JPEG) from imagescanner 109.

Data processor 101 further is in communication with a data store 102.Data store 102 may be a typical magnetic storage media capable ofstoring the digital images from digital image acquisition device 103and/or image scanner 109. Data store 102 may be used to store the imagesof the component parts of the eye temporarily until the images areprocessed by data processor 101, or permanently for long-term use anddiagnosis.

Data processor 101 further is in communication with a control unit 106and a display 107. Control unit 106 is a device that permits a user toflicker the digital images, while they are displayed on display 107.Also, control unit 106 may be a device or computer-implemented programthat automatically flickers among the images based on a rate defined bya user on control unit 106. Control unit 106 may be a keyboard, mouse,joystick, and/or microphone capable of communicating with data processor101 in response to commands from a user. As a user manipulates controlunit 106, data processor 101 receives and processes the commands fromcontrol unit 106. Data processor 101 then presents the images to beviewed on display 107, in accordance with the user's commands viacontrol unit 106.

FIGS. 2A and 2B provide a flowchart of describing the operation ofsystem 100 (as shown in FIG. 1) for judging changes in images of theoptic nerve head. Although the method shown in FIGS. 2A and 2B isspecific to changes in the optic nerve head for the purposes ofdetecting glaucoma, it should be appreciated that this method can beapplied to judging changes in images of any component part of the eyefor documentation, diagnosis and/or treatment of any disease orcondition of the eye.

As shown in FIG. 2A, in step 200, an examiner gathers availablenon-digital images of a patient's optic nerve head. These images may be35 mm photographic images and/or Polaroid images, for example. Thesenon-digital images may be acquired using a fundus camera, a slitlamp, orany other device capable of capturing images of the optical nerve. Thenon-digital images may then be scanned in step 201 into a digital formatusing image scanner 109, for example. In step 202, the examiner gathersany available digital images of a patient's optic nerve head. Thesedigital images may be acquired using digital image acquisition device103, for example, a digital findus camera, or any other device capableof acquiring digital images of the optic nerve. These digital imagesalso may be previously captured and located on a digital storage medium,for example a floppy disk or hard-disk drive. In step 203, the convertedimages and the digital images are provided to data processor 101. Theimages may be entered to data processor 101 directly from image scanner109 and/or from digital image acquisition device 103.

In step 204, data processor 101 acts to display the digital images ondisplay 107. In step 204, the examiner selects two or more images fromthe displayed images to be processed and superimposed by data processor101. The selected images may be based on the clarity of the images, andtheir similarity to the corresponding displayed images, or other desiredcharacteristics. Data processor 101 superimposes the selected displayedimages in step 206.

As shown in FIG. 2B, in step 207, the displayed images undergo digitalimage processing techniques, including polynomial warping, registering,and aligning to correct for differences in translation, rotation,magnification, and warping, for example. In particular, the imageregistration employs polynomial warping techniques that permit globaland non-global deformation of the images. Image registrationincorporating non-rigid, non-global deformations have not heretoforebeen applied for change detection successfully for eye images ingeneral, or optic nerve head images, in particular. In this way, a firstimage can be warped into registration with a second image. The aligningmay include non-rigid or rigid alignment techniques, or both. Suchdigital processing permits images that are incomparable in theiroriginal form to be compared accurately for discernment of stability orchange for the purposes of documenting, diagnosing and/or managing eyediseases and conditions. These digital processing techniques have beendefined in the following references, incorporated herein by reference:Berger, Quantitative, image sequence analysis of fundus fluoresceinangiography, Ophthalmic Surgery & Lasers 1999; 30:72-73; Shin, Javornik,and Berger, Computer-assisted, interactive fundus image processing formacular drusen quantitation, Ophthalmology 1999; 106: 1119-1125, andBerger J W et al Computerized stereochronoscopy and alternation flickerto detect optic nerve head contour change, Ophthalmology 2000; 107:1316-1320. It should be appreciated that the invention may include othertypes of processing necessary to permit intelligent unambiguouscomparison of the images.

In step 208, once the images are processed by data processor 101, theexaminer uses control unit 106 to alternate back-and-forth among theimages (ie., “alternation flicker”). In this way, the examiner mayselectively superimpose the images on top of each other, for example inchronological order in order to detect a progression of change in theimage. This “alternation flicker” process facilitates detection ofcontour change (or no change) to the eye image or optic nerve byallowing the examiner to continuously compare various characteristics ofthe nerve including vessel position and orientation. In other words,such alternation flicker permits the selected images to be superimposedon top of each other, and thus facilitates the examiner's ability todetect changes among the images of the component parts of the eye.

In step 209, the examiner decides whether the registration accuracy ofone or more of the images is satisfactory. If it is not satisfactory,the examiner may return to step 207 to perform additional imageprocessing on the individual images. Once satisfied with theregistration accuracy, the examiner determines whether another availableimage will improve the accuracy of the diagnosis in step 209. If theexaminer determines that another image should be selected, the examinerreturns to step 206 (as shown in FIG. 1) to select other images. If onthe other hand, the examiner is satisfied with the selected images andtheir registration accuracy, in step 210, the examiner decides whetherthere is a contour change in the patient's optic nerve head, at step211. The presence of change or no change in optic nerve head contour iscrucial for diagnosis and management of glaucoma, and is vital fordocumentation, diagnosis and/or management of other eye diseases basedon changes detected in images of the eye or its components.

Those skilled in the art will appreciate that numerous changes andmodifications may be made to the preferred embodiment of the inventionand that such changes and modifications may be made without departingfrom the spirit of the invention. For example, it should be understoodthat the invention may facilitate the detection of any changes in imagesof any component of the eye. It should also be understood that FIGS. 2Aand 2B demonstrate just one of the many possible components of the eyethat may be adjudged by the invention. Moreover, it should beappreciated that the invention is not limited to any componentsdescribed herein. It is therefore intended that the appended claimscover all such equivalent variations as fall within the true spirit andscope of the invention.

What is claimed is:
 1. A computer-implemented method of judging changesin components of an eye, comprising the steps of: acquiring at least twodigital images of components of the eye; displaying said digital imageson a computer-driven display; superimposing said digital images on saidcomputer-driven display; processing at least one of said digital imagessuch that said superimposed images may be compared; and flickering amongsaid superimposed digital images.
 2. The computer-implemented method ofclaim 1, wherein said step of processing includes the step of aligningsaid digital images.
 3. The computer-implemented method of claim 2,wherein said step of aligning said digital images includes the steps ofregistering and warping said digital images.
 4. The computer-implementedmethod of claim 1, further comprising the step of detecting changesamong said flickered, superimposed digital images so as to diagnose,document, and manage a condition of the eye as a function of saiddetected changes.
 5. A system for judging changes in components of aneye, comprising: a data processor for receiving and superimposingdigital images of components of the eye, and for processing said digitalimages to facilitate comparison among said images; a display device incommunication with said data processor, wherein said display devicedisplays said digital images and said superimposed images; and a controlunit in communication with said data processor, wherein said controlunit flickers among said superimposed images.
 6. The system of claim 5,further comprising an image scanner in communication with said dataprocessor for converting photographic images of components of the eyeinto said digital images.
 7. The system of claim 5, further comprising adigital image acquisition device in communication with said dataprocessor for acquiring said digital images.
 8. A computer-readablemedium having computer-executable modules, comprising: an input modulefor receiving digital images of components of the eye; a video modulefor superimposing said digital images and for displaying saidsuperimposed digital images on a display; and a control module forflickering among said superimposed digital images.
 9. Thecomputer-readable medium of claim 8, further comprising an imageprocessing module for processing at least one of said images.
 10. Thecomputer-readable medium of claim 8, further comprising a data storagemodule for storing said digital images.